The unique design of the Wilcoxon Research model F4/F7 combines a high-frequency piezoelectric vibration exciter (model F7) encircled by a low-frequency electromagnetic vibration exciter (model F4). Units incorporate a transducer base, containing a force gauge for test structure force monitoring; and an accelerometer, for measuring resultant motion. Transducer signals can be fed into either read-out equipment or signal conditioners. The model F4 electromagnetic vibration generator provides low frequency excitation from 10 Hz to 7,500 Hz, whereas the model F7 piezoelectric vibration generator produces vibrational forces over a high frequency range of 500 Hz to more than 20 kHz, resulting in the net capability to provide high force-to-weight output and a continuous sweep from low to high frequencies of 10 Hz to more than 20k Hz, with excitation capabilities across the entire audio range.
The model F7 contains a stack of piezoelectric plates which requires a voltage step-up (impedance matching via matching network) for high force output levels. The model F4 includes an air-cooling feature, allowing it to be run at higher output levels for extended periods without overheating. Its lightweight coil and bobbin are rigidly attached to the F7 generator, and incorporate use of heavy cylindrical magnets, which are suspended by two rubber diaphragms. The added dynamic weight is relatively low, since the rubber suspended weight does not affect axial or rotational inertia of the vibration generator core above its 30 Hz system resonance frequency. In addition, the compact, lightweight model F4/F7 shaker can easily be attached directly to a test structure in any position without external supports. Two power amplifiers are required to provide a continuous sweep. Input and output cables are provided.
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